"They are writhing, holding their stomach, complaining of really bad abdominal pain and nausea," said Dr.

"That's when we know we may have a case of cannabis hyperemesis syndrome, or CHS."

A bizarre condition

Cannabis hyperemesis syndrome burst upon the medical scene in 2004, when a group of Australian researchers wrote about 19 chronic marijuana users who had repeated episodes of abdominal pain and retching.

"Patients often say, 'You know, it's always in the evening when I get this nausea, vomiting,'" Wang said.

"That's not entirely clear," said Wang, who is also an associate professor of pediatrics at the University of Colorado Anschutz Medical Campus in Aurora, Colorado.

Tetrahydrocannabinol, or THC, the main psychoactive compound in weed, has access to the body's pain receptors, so one theory is that the distracting sensation of the extreme heat interrupts the pain cycle, thus easing symptoms.

To compound the strangeness of the new disorder, THC and other cannabinoids in the marijuana plant have been used for pain relief -- paradoxically relieving nausea and vomiting in cancer patients undergoing chemotherapy.

But CHS is so new that it doesn't have a medical diagnosis or insurance billing code, Wang said, making it "a moving target."

To do research, scientists look at medical records for reported cases of repetitive vomiting and compare those to marijuana usage in an area.

Between 2005 and 2014 when only medical marijuana was legal in most states, a 2020 study found nearly one in five people hospitalized for cyclical vomiting in the US reported concurrent cannabis use.

As of April, 17 states and the District of Columbia have legalized recreational marijuana for adults, while three dozen states and several territories have medical marijuana laws on the books, according to the Pew Research Center.

A Pew survey found the majority of US adults (60%) say marijuana should be legal for medical and recreational use.